1. Field of the Invention
The present invention relates to a process for producing a silicone-treated powder, more specifically relates to a silicone-treated powder obtained by coating a silicone compound having an Si—H group on the surface thereof and polymerizing the silicone on the surface thereof by heat treatment to obtain water repellency and to eliminate almost all the residual Si—H groups on the coating, to thereby be able to be formulated into various cosmetics, and superior in stability in a product, and a production process thereof.
2. Description of the Related Art
There have been various methods for giving hydrophobicity to a powder in the past. Using the hydrophobicity of silicone oil is well known.
The silicone compounds usable for providing hydrophobicity are those having an organohydrogenpolysiloxane chain in the molecule and also sometimes having a diorganopolysiloxane chain in the molecule or a mixture of organohydrogenpolysiloxane and diorganopolysiloxane. When these compounds are coated on the surface of a powder, the Si—H group bonded portion of the organohydrogenpolysiloxane molecule reacts with the moisture etc. in the air due to the surface activity of the powder, and the Si—OH groups produced react with the Si—H groups of the other adjacent molecules, or the Si—OH groups react among themselves to cause cross-linking and polymerization and to form a silicone film.
However, with heat treatment in the air at about 200° C. after coating organohydrogenpolysiloxane on the surface of a powder, the residual Si—H groups are not completely eliminated, while the cross-linking reaction of the molecules themselves proceeds to a certain extent. On the other hand, with heating at 500° C. or more, the silicone starts to burn and is converted to silica (see Japanese Unexamined Patent Publication (Kokai) No. 11-199458, the treatment for coating silicon oxide by heating at a temperature of 600 to 950° C.
The residual Si—H groups react with the moisture in the air or the moisture, alcohol, amines, etc. in makeup products over a long period of time to cause the production of hydrogen and form new siloxane bonds, and therefore, if the above treated powder is used as it is for cosmetics, coating compositions, toners, inks, containers, and ingredients of various other compositions, various problems will sometimes be caused in the compositions.
For example, in the case of cosmetics, there is a risk of generation of hydrogen in the production process, the containers may swell with the elapse of time after filling the product into containers, and the product may harden and crack. In the case of coating compositions, the problem of deterioration of the container sometimes occurs.
To reduce the above-mentioned residual Si—H groups, for example, the method of Japanese Unexamined Patent Publication (Kokai) No. 63-113081 (i.e., Japanese Patent No. 1635593) (i.e., the addition of a compound having unsaturated hydrocarbon group to residual Si—H groups by hydrosilylation reaction), the method of Japanese Unexamined Patent Publication (Kokai) No. 8-192101 (i.e., the substitution of residual Si—H groups by contact with water or lower alcohol), the method of Japanese Examined Patent Publication (Kokoku) No. 56-43264 (i.e., the mixture and pulverization of metal hydroxide serving as a catalyst for cross-linking and polymerization of organohydrogenpolysiloxane with a treated powder, then using mechanochemical reaction), etc. have been attempted.
The above methods are effective in their own right, but the processes are complicated, a long time is required, or relatively active functional groups are adsorbed on the surface, and therefore the powder is given an unpleasant smell etc.